142 GREAT MEN OF SCIENCE 



breathing of marine animals. This work was done in the 

 years 1760 to 1773, but great delay occurred in publication 

 in print, which first took place in 1777.^ 



Scheele not only discovered oxygen from pyrolusite, but 

 also made a very thorough examination of the latter sub- 

 stance. In the course of this he discovered chlorine gas (by 

 bringing pyrolusite in contact with hydrochloric acid) studied 

 the compounds of manganese, and discovered the compounds 

 of barium, which are generally contained in pyrolusite, but 

 had hitherto not been recognised. He showed that they 

 afford the best means for detecting sulphuric acid. How 

 thorough Scheele was in all his work is also shown by his 

 investigation of water. It had been assumed that pure water, 

 when boiled for a long time, turns into a solid substance. 

 Scheele, 'in order to see with his own eyes,' kept distilled 

 snow-water boiling in a glass vessel with a very long neck 

 for twelve days. The water became somewhat milky and 

 formed a white precipitate, but Scheele was able to show that 

 both the precipitate and also the substances found dissolved 

 in the water, were simply constituents of the glass, and that 

 the vessel had become etched upon its internal surface as 

 far as the water reached. No transformation of the water 

 had therefore taken place, and our knowledge of this liquid 

 was thus further advanced. 



Scheele was also the first to investigate the various acids 

 of the vegetable kingdom, such as tartaric acid, malic acid, 

 citric acid, oxalic acid; and also uric acid and lactic acid, 

 finding how to separate them by precipitation and trans- 

 formation. He also discovered glycerine, as a special 

 substance contained in all fats, and separated it from 

 them by means of litharge. He also discovered molybdic 

 and tungstic acids, and investigated them as special 



^ The first proved entry by Scheele concerning oxygen in his labora- 

 tory notes dates from November 1772 (compare Nordenskjold, tb., 

 pages 462-466). Bunsen described in his lectures the day on which 

 oxygen was discovered as the 'real birthday of chemistry.* 



